Adobe is a clay-rich mixture of straw and clay which has been used as building material for people to shelter from the wind and rain for thousands of years. For this kind of structural composites, clay provides a good barrier property for light, rain and heat, and fibrous straw provides strength and durability that prevents cracking, increases its insulativity and makes it lighter.
In nature there are many organisms with this kind of polymer-ceramic particle composite structure. Normally, they have excellent strength and toughness. For example, nacre, originating from the shell of abalone, with 1-5% protein and aragonite, has a tensile strength of 140-170 MPa, a Young's modulus of 60-70 GPa, and a three point bending of 350-1240 J·m−2 depending on its hydration state. As a result, many methods have been reported so far to simulate the nacre “brick and mortar” structure, including sequential deposition, supra-molecular self-assembly (dip-coating), crystallization on self-assembled layers, crystallization beneath Langmuir monolayers, layer-by-layer self-assembly, casting procedure and so on. The best results were achieved by Tang et al, who produced ultra strong composite layers with thickness of about 5 μm by alternately dipping a glass slide in polyelectrolyte and clay platelet suspension. However, such method requires really long assembly time because each cycle deposited about 24 nm. Recently, Tang et al. developed a new method called “exponential growth” LBL. The self-assembly time was shortened, but it still takes 1000 min to obtain a film with thickness of 200 μm. F. Mizukami et al used a casting procedure to prepare flexible transparent clay films with the thickness of 3-200 μm. The preparation was markedly simplified and also the films have good heat-resistant and high gas-barrier properties. However, the tensile strength of the material is only 25 MPa. The weak strength will be an obstruction for further application of this kind of clay films. The casting procedure is still a time-consuming method due to the slow evaporating of the water. It is difficult to reproduce the brick and mortar microstructure of nacre in a convenient way.
As known, in the case of nacre, only 1-5% of the proteins act as the binder additive. For artificial nacre, water-soluble polymers (WSPs) such as polyelectrolytes, polymer sodium salt or PVOH were used as the binder additive instead of the protein in the natural nacre. There is a strong electrostatic or hydrogen bonding interaction between WSPs and inorganic clay platelets. However, in contrast to the low content of protein found in the nacre, typically the content of WSPs used in the artificial nacre is more than 50 wt. %. Additionally, most of the WSPs used today are non-biodegradable, and also WSPs have bad water-resistance or solvent-resistance.